This invention relates to a Fourier spectrophotometric device and in particular to a device for obtaining spectrum using interference fringes spatially focused.
In general, spectrum is used in qualitative analysis for investigating the kind of unknown components in a sample or in measurements for obtaining the quantity of known components, so-called quantitative analysis and indicates the relation between the wavelength or wave number and the light intensity.
As a Fourier spectrophotometric device related to this invention, a Fourier spectrophotometric device, in which interference fringes spatially focused are detected by means of a photo-diode array and for which no mechanical scanning is necessary, is described in Appl. Opt. 24 (1985) pp. 3702-3706.
By the related techniques, in order to obtain an interferogram containing no DC-component, so-called clean interferogram from interference fringes, a plane mirror in a Sagnac type common path interferometer is tilted in the vertical direction so that the interference fringes disappear, only the background (DC-component) signal is taken-out and stored; the inclination of the plane mirror stated above is adjusted suitably so as to form interference fringes; signals of an interferogram superposed on the background are measured; and the stored background signal is subtracted therefrom.
According to this method, since a plane mirror, which is a constituent of the interferometer, for which extremely severe optical adjustment is necessary, is moved mechanically, there are problems in reproducibility and reliability. Further, even if the background signal can be obtained by a method other than the mechanical method, it is necessary to scan the photo-diode array at least 2-times by means of electronic means.